Angioplasty is a frequently used procedure for treating blockages in patients' blood vessels. With an angioplasty procedure, a balloon catheter is inserted into an obstructed blood vessel. An inflatable balloon, typically at the distal end of the catheter, is aligned with a stenosis effecting an obstruction in the vessel. Fluid is directed through an inflation lumen into the balloon to inflate the balloon and thereby extend the stenosis to provide an enlarged passage through it.
Prior to performing an angioplasty procedure, a physician will typically fluoroscopically examine the patient to locate a stenosis to be treated and determine its diameter and its length longitudinally of a blood vessel being obstructed by it. Balloon catheters are manufactured with balloons of a variety of sizes. A physician, having determined the axial length and diameter of a stenosis, will select a catheter of appropriate size and then perform the angioplasty procedure.
Where a patient has two or more stenoses, the lengths of the stenoses typically will be different. When such a condition is confronted, in the past it has been necessary for a physician to perform angioplasty with a catheter selected to be appropriate for one stenosis, remove that catheter from the patient following treatment of the one stenosis and then insert a second and different catheter to treat a second stenosis in order that catheters of appropriate size will be used for treatment of each stenosis. Such a procedure is time consuming and expensive due to the need for use of two catheters. In addition, there is a considerable increase in patient risk because of the time consumed and the complexity of the procedure. Clearly it would be desirable to be able to treat such conditions with a single insertion of one catheter.
Since balloons of prior catheters are made to fixed predetermined lengths, it is usually necessary to select a catheter of an axial length greater than a stenosis to be treated to assure expansion of the entire stenosis. As a consequence trauma is caused in adjacent less diseased regions. Accordingly, it would also be desirable to be able to adjust the effective length of a balloon to treat the stenosis while minimizing trauma in adjacent regions.
Where a total occlusion of an artery is present, success rates with angioplastic procedures have been very low. Where bridging collaterals or side branches to the occluded artery are present, an angioplastic guide wire tends to follow the path of least resistance, rather than to work its way through to the occlusion. Slightly higher success rates have been achieved with so called "olive" wires, that is guide wires each with an enlarged, somewhat olive shaped, distal end as described in an article by Meier et al. entitled "Magnum/Magnarail versus conventional systems for recanalization of chronic total coronary occlusions: a randomized comparison" published in the May 1992 issue of American Heart, pgs. 1182-6. Such guide wires have achieved somewhat better rates of success because an olive tends to prevent the wire from entering collaterals.
Prior procedures seeking to open occlusions with catheters have applied luminal forces to the atheromas. If excessive axial force is applied to an atheroma, it can create high shear forces at the atheroma-vessel interface. The shear forces tend to tear the atheroma lose from the arterial wall. Accordingly, it would be desirable to have angioplasty materials and procedures which would exert a more selective "digging" action in the center of an occluded vessel while preserving the integrity of the arterial wall.
When a self expanding stent is implanted in an artery, the stent is typically collapsed and then surrounded by an annular skin. Once the stent has been positioned within an artery at a location where it is to be implanted, the skin is pulled from around the stent as an axial force is applied to the stent to resist the pulling action. With such an arrangement, the initial force required to strip the surrounding skin is quite high because of the frictional resistance between the skin and the stent. Accordingly, this implantation procedure has limited the lengths of such expansible stents that can be implanted and suffered from other shortcomings as well.
With certain conditions it is desirable to administer drugs to vessel walls for treatment of an existing condition. Hydrogel coated balloons are utilized as delivery systems. Elaborate means are required to protect vessel surfaces from the coating as a coated balloon is deployed in a vessel to be treated. Clearly it would be desirable to have a simplified mechanism to protect vessel walls as a balloon coated with a medication is delivered to a location to be treated.